Dynamic damper and propeller shaft

ABSTRACT

This invention provides a dynamic damper  10,  in which convex portions  21  protruded in the direction of the inside diameter are provided at plural positions along the circumference of the outer pipe  20,  and an elastic body  40  is held between the convex portion  21  and the outer circumference of the weight  30.  A stopper portion  32  which is capable of engaging the convex portion  21  of the outer pipe  20  in the axial direction of the pipe is provided on the weight  30.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a dynamic damper and a propellershaft.

[0003] 2. Description of the Related Art

[0004] There are dynamic dampers, which reduce vibration of anautomobile driving power-transmitting member, such as a propeller shaft,in order to reduce vehicle vibration and mechanical noise. Such dynamicdampers include an outer pipe, a weight disposed inside the outer pipeand an elastic body disposed between the outer pipe and the weight. Thisdynamic damper is pressed into a hollow shaft constituting the propellershaft and is fixed thereto.

[0005] In the dynamic damper disclosed in Japanese Utility ModelApplication Publication No. H7-29324, an elastic body is disposed in anannular space between an outer pipe and a weight, and a rod-like elasticinterposed portion is provided so as to extend in the radius directionat each of a plurality of positions (five positions) in thecircumferential direction of the annular space.

[0006] Conventional technology has the following problems.

[0007] (1) The elastic body is so supported that an end of each elasticinterposed portion is abutted to an inner face of the outer pipe whilethe other end portion thereof is abutted to an outer face of the weight.For this reason, there is a concern that the elastic body may receiverepeated compression in the radius direction and shearing stress in therotation direction resulting from vibration generated when the propellershaft is revolved, so that it may become damaged with cracks. If theweight deflects largely laterally relative to the outer pipe, or dropsdue to cracks in the elastic body, the dynamic damper loses its initialvibration resistant characteristic.

[0008] (2) As above-described in (1), there is a concern that theelastic body may receive repeated compression in the radius directionand shearing stress in the rotation direction based on vibration of thepropeller shaft, so that it may become damaged with cracks. Thus, thedynamic damper may lose its durability.

[0009] (3) The dynamic damper must be pressed into and fixed to a hollowshaft firmly so as not to be deflected by acceleration/deceleration andvibration accompanied by a rotation of the propeller shaft. In case of atype in which the entire circumference of the outer pipe is pressed intothe hollow shaft directly, both the members cannot be fitted to eachother easily due to the existence of dimensional error between theinside diameter of the hollow shaft and the outside diameter of theouter pipe. Thus, a high dimensional accuracy is needed. Further,because the outer pipe is pressed into the hollow shaft with the entirecircumference sliding on the inner face of the same hollow shaft, acontact area of the outer pipe relative to the inner face of the hollowshaft is increased. Therefore, a large press-in operation force isrequired, which leads to an increase of cost for production equipment.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide a dynamicdamper, which allows a weight to be securely accommodated in an outerpipe.

[0011] An object of the present invention is to provide a dynamic damperhaving improved durability and reliability.

[0012] Another object of the present invention is to press a dynamicdamper into a hollow shaft easily, to be fixed thereto stably.

[0013] According to the present invention, there is disclosed a dynamicdamper comprising an outer pipe, a weight disposed inside the outer pipeand an elastic body interposed between the outer pipe and the weight.

[0014] Convex portions protruded in the direction of the inside diameterare provided at a plurality of positions along the circumference of theouter pipe, and an elastic body is held between the convex portion andthe outer circumference of the weight.

[0015] A stopper portion, which is capable of engaging the convexportion of the outer pipe in the axial direction of the outer pipe byrelative moving of the outer pipe and the weight, is provided on theweight.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be more fully understood from thedetailed description given below and from the accompanying drawings,which should not be taken to be a limitation on the invention, but arefor explanation and understanding only.

[0017] The drawings:

[0018]FIGS. 1A and 1B show a dynamic damper, where FIG. 1A is a frontview thereof and FIG. 1B is a sectional view taken along the line B-B;

[0019]FIG. 2 is a perspective view showing a dynamic damper; and

[0020]FIGS. 3A and 3B show a modification of the dynamic damper whileFIG. 3A is a front view thereof and FIG. 3B is a sectional view takenalong the line B-B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Reference numeral 10 in FIGS. 1A and 1B denotes a dynamic damper10, which is pressed into a hollow shaft 2 of an automobile 10 propellershaft 1 and disposed at a predetermined position thereof in the axialdirection. The dynamic damper 10 reduces vibration of the propellershaft 1 so as to reduce vehicle body vibration and mechanical noise.

[0022] The dynamic damper 10 comprises an outer pipe 20, a weight 30 andan elastic body 40.

[0023] The outer pipe 20 is formed by bending a metallic pipe such asthin steel pipe, in the form of an irregularly shaped cylinder. Thisouter pipe 20 contains convex portions 21 protruded in the direction ofits inside diameter at a plurality of positions (5 positions in thisspecification) along the circumferential direction. More specifically,in the outer pipe 20, the convex portions 21 are formed by bending theplural portions along the circumferential direction of a round pipe inthe direction of the inside direction with a press while remainingportions are kept as circular portions 22 (circular portion 22 havingsubstantially the same curvature of a hollow shaft 2). An end face ofthe convex portion 21 of the outer pipe 20 acts as a round pressing face21A to the outer circumferential portion of an elastic body 40. Theoutside diameter of the outer pipe 20 under the free state formed by thecircular portions 22 is set larger than the inside diameter of thehollow shaft 2. The outside diameter can be contracted elastically fromthe free state due to the elastic distortion characteristic possessed bythe bent portion of the convex portion 21.

[0024] The weight 30 is formed of a metallic rod such as steel rod inthe form of a short cylinder, such as a circular cylinder. The weight 30has annular grooves 31 provided in the entire circumference for loadingthe elastic body 40. The weight 30 is disposed inside the outer pipe 20coaxially with the outer pipe 20. The weight 30 is wider than the outerpipe 20 (FIG. 1B).

[0025] The elastic body 40 is formed in an annular form and is loaded onthe entire circumference of the annular groove 31 in the weight 30between the outer pipe 20 and the weight 30. The outer circumference ofthe elastic body 40 is a circular face continuous along the entirecircumference, which is larger than the outside diameter of the weight30. The elastic body 40 is formed of synthetic rubber and bonded to theouter pipe 20 and the weight 30 by vulcanizing.

[0026] The dynamic damper 10 holds the elastic body 40 by sandwichingthe elastic body 40 on the weight 30 with the end pressing faces 21A ofthe convex portion 21 of the outer pipe 20 from the radiation direction.Also, the dynamic damper 10 sandwiches the outer peripheral portion 41of the elastic body 40 between the end pressing faces 21A in thecircumferential direction, of the convex portions 21 adjacent in thecircumferential direction of the outer pipe 20. The end pressing face21A of each convex portion 21 is buried in a predetermined depth in theouter peripheral portion 41 of the elastic body 40. The outer peripheralportion 41A is sandwiched between the end pressing faces 21A of theconvex portion 21.

[0027] In the dynamic damper 10, the diameter A of an inscribed circlein contact with each convex portion 21 of the outer pipe 20 is setsmaller than the outside diameter B of each of right/left stopperportions 32 located on both edge portions of an annular groove 31 in theouter circumference of the weight 30. The stopper portions 32 providedon the weight 30 are capable of engaging with the convex portion 21 inthe axial direction on the outer pipe 20 if the outer pipe 20 and theweight 30 move relative to each other.

[0028] In the dynamic damper 10, the outside diameter of the outercircumference of the weight 30 is decreased gradually from each of theright/left stopper portions 32 up to each end face in the axialdirection so as to provide an insertion guide face 33 for the outer pipe20. The convex portion 21 of the outer pipe 20 slides on the insertionguide face 33 provided on the stopper portion 32 of the weight 30 so asto expand its diameter elastically, and then surpasses the stopperportion 32. This enables the insertion of the convex portion 21 into theannular groove 31 in the outer circumference of the weight 30.

[0029] To produce the dynamic damper 10, the elastic body 40 is formedintegrally by injection molding by pouring rubber into a mold in whichthe outer pipe 20 and the weight 30 are disposed. Alternatively, theelastic body 40 may be formed separately and subsequently bonded to theouter pipe 20 and/or the weight 30.

[0030] This embodiment has the following operations.

[0031] (1) The weight 30 is provided with the stopper portion 32 whichis capable of engaging the convex portion 21 of the outer pipe 20 in theaxial direction. Therefore, if the elastic body 40 happens to be damagedwith cracks so that the weight 30 tends to move laterally relative tothe outer pipe 20, the stopper portion 32 of the weight 30 engages theconvex portion 21 of the outer pipe 20 so as to prevent the weight 30from moving largely laterally, or from dropping. The weight 30 isaccommodated inside the outer pipe 20 securely, so that the initialvibration resistance of the dynamic damper 10 is secured.

[0032] (2) The dynamic damper 10 is provided with the annular elasticbody 40 mounted in the entire annular space between the outer pipe 20and the weight 30. Further, the outer circumferential portion 41A of theelastic body 40 is sandwiched and held between the convex portion 21protruded in the direction of the inside diameter of the outer pipe 20and adjacent the convex portion 21 in the circumferential direction.Consequently, upon repeated application of load due to compression inthe radius direction from the weight 30, shearing stress in the rotationdirection and the like based on rotary vibration of the propeller shaft1 is distributed widely to respective portions of the elastic body 40.Thus, concentration of stress on the elastic body 40 is suppressed so asto prevent cracking damage, thereby improving the durability of thedynamic damper 10.

[0033] (3) Because the convex portions 21 are formed by bendingrespective portions of the outer pipe 20 in the circumferentialdirection in the direction of the inside diameter, elastic distortioncharacteristics in the radius direction can be obtained at the bentportions of the convex portions 21. Therefore, when the dynamic damper10 is pressed into the hollow shaft 2, dimensional error between theinside diameter of the hollow shaft 2 and the outside diameter of theouter pipe 20 is absorbed by elastic distortion of the outer pipe 20 andelastic distortion of the elastic body 40, thereby allowing the dynamicdamper to be pressed into the hollow shaft 2 easily. After being pressedin, the dynamic damper can be fixed firmly to an inner face of thehollow shaft 2 due to elastic restoration forces of the outer pipe 20and the elastic body 40.

[0034] (4) When the outer pipe 20 is pressed into the hollow shaft 2,only the plural circular portions 22, except the bent portions of theconvex portions 21 on the entire circumference of the outer pipe 20, rubthe hollow shaft 2. As a result, the contact area of the outer pipe 20with the inner face of the hollow shaft 2 is decreased. The result isthat the press-in operation force is also decreased which leads toreduction of cost on production equipment.

[0035] (5) When assembling the outer pipe 20 with the weight 30, theconvex portion 21 of the outer pipe 20 slides on the insertion guideface 33 provided on the stopper portion 32 of the weight 30 while beingelastically enlarged. This enables the convex portion 21 to surpass thestopper portion 32. Consequently, the convex portion 21 will fit to theouter circumference of the weight 30. After that, the elastic body 40 isformed by pouring rubber between the outer pipe 20 and the weight 30.Thus, production and assembly of the dynamic damper 10 can befacilitated.

[0036] (6) The aforementioned (1) to (5) are achieved in the propellershaft 1, so that the weight 30 can be accommodated securely inside theouter pipe 20 constituting the dynamic damper 10. Additionally, thedurability of the dynamic damper 10 can be improved. Further, thedynamic damper 10 can be pressed into the hollow shaft 2 easily andfixed thereto in a stable condition.

[0037]FIGS. 3A and 3B show a modification of the dynamic damper. FIG. 3Ais a front view thereof and FIG. 3B is a sectional view taken along theline B-B.

[0038] The dynamic damper 100 of FIGS. 3A and 3B have the followingstructure as well as the same basic structure as the dynamic damper 10shown in FIG. 1A to FIG. 2.

[0039] In the dynamic damper 100, the diameter A1 of an inscribed circle(inscribed circle in contact with portions excluding both end portionsin which the insertion guide face 23 of the convex portion 21 isprovided) in contact with each convex portion 21 of the outer pipe 20 isset smaller than the outside diameter B of each of the right/leftstopper portions 32 located on both edge portions of an annular groove31 in the outer circumference of the weight 30. The stopper portions 32provided on the weight 30 are capable of engaging with the convexportion 21 on the outer pipe 20 in the axial direction if the outer pipe20 and the weight 30 move relative to each other.

[0040] In the dynamic damper 100, the outside diameter of the outercircumference of the weight 30 is decreased gradually from each of theright/left stopper portions 32 up to each end face in the axialdirection so as to provide an insertion guide face 33 for the outer pipe20. The convex portion 21 of the outer pipe 20 slides on the insertionguide face 33 provided on the stopper portion 32 of the weight 30 so asto expand its diameter elastically and then surpasses the stopperportion 32. This enables the insertion of the convex portion 21 into theannular groove 31 in the outer circumference of the weight 30.

[0041] Further, in the dynamic damper 100, the diameter of the inscribedcircle in contact with each of both end portions along the axialdirection of the convex portion 21 of the outer pipe 20 is increased upto A2 (A2>B) gradually so as to provide an insertion guide face 23 forthe weight 30. The convex portion 21 of the outer pipe 20 makes theinsertion guide face 23 provided at the convex portion 21 of the outerpipe 20 slide against the insertion guide face 33 provided on thestopper portion 32 of the weight 30. This enlarges the diameter of theconvex portion 21 elastically to surpass the stopper portion 32 so thatit fits to the annular groove 31 in the outer circumference of theweight 30. In this case, alignment of both axes of the outer pipe 20 andthe weight 30, which needs to be executed before the insertion, isfacilitated by the two guide faces.

[0042] Therefore, the dynamic damper 100 has the following operations.

[0043] When assembling the outer pipe 20 with the weight 30, the convexportion 21 of the outer pipe 20 makes the insertion guide face 23provided at the convex portion 21 of the outer pipe 20 slide against theinsertion guide face 33 provided on the stopper portion 32 of the weight30 to enlarge the diameter of the convex portion 21 elastically tosurpass the stopper portion 32. In this manner, it is fit to the annulargroove 31 in the outer circumference of the weight 30. After that, theelastic body 40 is formed by pouring rubber between the outer pipe 20and the weight 30. Consequently, production and assembly of the dynamicdamper 100 are facilitated.

[0044] As heretofore explained, embodiments of the present inventionhave been described in detail with reference to the drawings. However,the specific configurations of the present invention are not limited tothe embodiments, but those having a modification of the design withinthe range of the present invention are also included in the presentinvention. For example, the dynamic damper of the present invention canbe applied to a driving power transmitting member other than thepropeller shaft.

[0045] As described above, the dynamic damper according to the presentinvention allows the weight to be securely accommodated inside the outerpipe. Further, according to the present invention, the durabilityreliability of the dynamic damper can be improved. Further, according tothe present invention, the dynamic damper can be pressed into the hollowshaft easily and fixed thereto in a stable condition.

[0046] Although the invention has been illustrated and described withrespect to several exemplary embodiments thereof, it should beunderstood by those skilled in the art that the foregoing and variousother changes, omissions and additions may be made to the presentinvention without departing from the spirit and scope thereof.Therefore, the present invention should not be understood as limited tothe specific embodiment set out above, but should be understood toinclude all possible embodiments which can be embodied within a scopeencompassed and equivalents thereof with respect to the features set outin the appended claims.

What is claimed is:
 1. A dynamic damper comprising an outer pipe, aweight disposed inside the outer pipe and an elastic body interposedbetween the outer pipe and the weight, convex portions protruded in thedirection of the inside diameter are provided at a plurality ofpositions along the circumference of the outer pipe, and an elastic bodyis held between the convex portion and the outer circumference of theweight, and a stopper portion disposed on the weight, the stopperportion being engagable with the convex portion of the outer pipe in theaxial direction of the outer pipe by relative moving of the outer pipeand the weight.
 2. The dynamic damper according to claim 1, wherein theouter circumferential portion of the elastic body is nipped between theconvex portions adjacent each other of said outer pipe.
 3. The dynamicdamper according to claim 1, wherein the outer pipe is bent in thedirection of the inside diameter at plural portions along thecircumferential direction so as to form the convex portions.
 4. Thedynamic damper according to claim 2, wherein the outer pipe is bent inthe direction of the inside diameter at plural portions along thecircumferential direction so as to form the convex portions.
 5. Thedynamic damper according to claim 1, wherein the convex portion of theouter pipe slides on an insertion guide face provided on the stopperportion of said weight so as to enlarge elastically the diameter of theconvex portion to surpass the stopper portion so that it fits to theouter circumference of the weight.
 6. The dynamic damper according toclaim 2, wherein the convex portion of the outer pipe slides on aninsertion guide face provided on the stopper portion of said weight soas to enlarge elastically the diameter of the convex portion to surpassthe stopper portion so that it fits to the outer circumference of theweight.
 7. The dynamic damper according to claim 3, wherein the convexportion of the outer pipe slides on an insertion guide face provided onthe stopper portion of said weight so as to enlarge elastically thediameter of the convex portion to surpass the stopper portion so that itfits to the outer circumference of the weight.
 8. The dynamic damperaccording to claim 4, wherein the convex portion of the outer pipeslides on an insertion guide face provided on the stopper portion ofsaid weight so as to enlarge elastically the diameter of the convexportion to surpass the stopper portion so that it fits to the outercircumference of the weight.
 9. The dynamic damper according to claim 1,wherein the contact face of the convex portion with the outer peripheralportion of the elastic body is formed in the form of a round face. 10.The dynamic damper according to claim 1, wherein the weight is disposedinside the outer pipe and coaxially with the outer pipe.
 11. A propellershaft wherein the dynamic damper according to claim 1 is pressed intoand fixed to a hollow shaft.
 12. A propeller shaft wherein the dynamicdamper according to claim 2 is pressed into and fixed to a hollow shaft.13. A propeller shaft wherein the dynamic damper according to claim 3 ispressed into and fixed to a hollow shaft.
 14. A propeller shaft whereinthe dynamic damper according to claim 4 is pressed into and fixed to ahollow shaft.
 15. A propeller shaft wherein the dynamic damper accordingto claim 5 is pressed into and fixed to a hollow shaft.
 16. A propellershaft wherein the dynamic damper according to claim 6 is pressed intoand fixed to a hollow shaft.
 17. A propeller shaft wherein the dynamicdamper according to claim 7 is pressed into and fixed to a hollow shaft.18. A propeller shaft wherein the dynamic damper according to claim 8 ispressed into and fixed to a hollow shaft.
 19. A propeller shaft whereinthe dynamic damper according to claim 9 is pressed into and fixed to ahollow shaft.
 20. A propeller shaft wherein the dynamic damper accordingto claim 10 is pressed into and fixed to a hollow shaft.